suprachiasmatic nucleus
Master circadian pacemaker located in the hypothalamus that regulates biological rhythms.
Full Definition
The suprachiasmatic nucleus (SCN) is a small bilateral structure located in the anterior hypothalamus that serves as the master circadian clock in mammals. Composed of approximately 20,000 neurons, the SCN receives direct input from the retina via the retinohypothalamic tract, allowing it to synchronize internal biological rhythms with environmental light-dark cycles. The SCN regulates the timing of hormone release, including melatonin from the pineal gland and cortisol from the adrenal cortex, and coordinates circadian rhythms throughout the body through neural and hormonal signals.
Usage
Usage note: Can be abbreviated as SCN after first mention; 'supra-' prefix means 'above the optic chiasm'.
In Context
- "Lesions to the suprachiasmatic nucleus disrupted normal sleep-wake cycles in the research subjects." — Research study
- "The suprachiasmatic nucleus showed decreased activity in patients with delayed sleep phase syndrome." — Sleep study report